Armor penetrating, high-explosive projectiles, have been modified in recent years with respect to the location of the detonator within the shell casing with respect to the explosive charge, the shape of the charge itself and the shape of the ogive.
In particular, it has been discovered that by the shaping of the front portion of the explosive charge and causing its detonation at a point remote from the target surface, one can increase the penetration of the charge through armor plate to a greater extent than if the charge detonated at the surface of the target. However, certain physical parameters limit the distance of the charge from the forward end of the nose cone of the projectile.
Conventional artillery is limited by its design to specific lengths of shell and caliber of projectile. Therefore, to have a projectile of conventional, standard length is a necessity.
In the course of research it has been discovered that the optimum distance between the target surface and the front of the shaped charge in a projectile is about six to seven times the diameter of the forward face of the shaped charge. Having the charge further from the forward tip of the nose cone is certainly achievable with conventional designs by having the shaped charge located further and further from the tip of the nose cone but it quickly reaches the point of diminishing returns as far as efficiency is concerned because moving the forward face of the shaped charge further from the forward tip of the nose cone cuts down on the amount of charge which may be housed in the casing.
The problem being attacked is to find a simple mechanical device for causing detonation at the optimum distance from the target surface.